The ebay link that Ted provided is not an "old", "original", long tang, round knob Superposed stock with original buttplate, in high condition which is what we would like to find. Good luck.
True enough, but, looking doesn’t hurt. A Superposed is a production gun. There are about 600 of them for sale on GI alone at any one time. There are used stocks floating around, a guy can keep his eyes open, and perhaps find something that can be fitted.
Restocking a 12 gauge Superposed doesn’t appear to make financial sense from this juncture. Several have pointed this out. There are also links to capable wood guys that could make it happen, but, were it me, I’d be willing to give the looking process a bit of time, first.
Best,
Ted
